Bryan, cannot help with the arm as such, but some time ago I came across some info on making a dish your self..
It has all the info and measurements on it so with some ingenuity and gaffer tape you could make up something even from a piece of wood ( and no, this is not a joke or wind up ! )

LNB's are available for very little money from almost anywhere nowadays, so you should be able to get it sorted out quite easily with any luck.